Trunked radio repeater communication system including home channel aliasing and call grouping

ABSTRACT

A system for channel assignment in a trunked transmission communication system including a plurality of subscribers. A plurality of subscribers is provided home channel assignment to reduce collisions. A home channel alias is provided for home channel coverage where a designated home channel is unavailable. A system for call grouping is provided to avoid talk group splitting. A first check is used to determine if other channels are conducting communications with identical home and talk group information. A second check is available after a temporary channel assignment. In one system both the home channel aliasing and call grouping are performed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/058,687, filed on Apr. 10, 1998, which claims the benefit ofprovisional patent application U.S. Ser. No. 60/047,843, filed May 28,1997, the specifications of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to trunked radio communicationssystems, and in particular to a method and apparatus for trunkedcommunication systems including home channel aliasing and call grouping.

BACKGROUND OF THE INVENTION

Mobile radio communication systems provide for two way radiocommunications between a central control station and a fleet of cars,trucks, or other vehicles. Typical users of mobile radio communicationsystems include, for example, police departments, fire departments, taxiservices and delivery services. Present mobile radio communicationsystems can be configured to provide for radio communications betweenthe control station and all vehicles in a fleet, between the controlstation and selected vehicles in the fleet, or between differentindividual vehicles or groups of vehicles within a fleet.

Conventional mobile radio communication systems are typically organizedwith a number of vehicles and a control station assigned to a singlecommon channel for a given coverage zone. A user assigned to the commonchannel must wait until no one else is transmitting on that channelbefore sending a message, because only one transmission at a time can beprocessed by a single channel. Even when a transmission is addressed toonly one user in a conventional system (and therefore not heard by otherusers), the other users in the system must wait until that transmissionis completed before they can use the system to communicate.

Mobile radio communication systems using transmission trunking are animprovement over conventional mobile radio communication systems in thattrunked systems enable two or more users to communicate on the system atthe same time. For instance, the dispatch console in a transmissiontrunked communication system can be communicating with one of thevehicles in the fleet; while, at the same time, two other vehicles inthe fleet can be using the same trunked system to communicate with eachother. Transmission trunked communication systems group a number ofchannels for the same coverage zone together into a single audiocommunication system, with each channel accessible to each user in thesystem. Because each user will only need to communicate over the trunkedsystem part of the time, and because it is unlikely that all users willneed to communicate at precisely the same time, the number of channelsassigned to a trunked system group can always be less than the number ofusers allocated to that trunked system group.

The United States Federal Communications Commission (FCC) has assigned600 channels in the 800 MHZ band for trunked land mobile use. Eachchannel is comprised of a pair of assigned frequencies, a mobiletransmit frequency and a repeater transmit frequencies. Mobile transmitfrequencies are 806-821 MHZ, with the repeater transmit frequenciesexactly 45 MHZ above the corresponding mobile transmit frequency, or851-866 MHZ. Channel spacing is 25 KHz, with the maximum alloweddeviation between channels being ±5 KHz. In September 1987, the FCC alsoallocated 399 channels in the 900 MHZ band for trunked land mobile use.Mobile transmit frequencies are 896-901 MHZ, with the repeater transmitfrequencies exactly 39 MHZ above the corresponding mobile transmitfrequency, or 935-940 MHZ. Channel spacing is 12.5 KHz, with the maximumallowed deviation between channels being ±2.5 KHz.

In transmission trunked communication systems, a signaling protocol isused to send and receive control signals among users on each channel inthe trunked system and a switching protocol is used to establish whichchannels those users will be communicating over. The preferredconventional transmission trunked communication system uses a signalingprotocol that transmits the control signals in the subaudio bandsimultaneously with the transmission of voice or data informationsignals. Signaling protocols that can communicate control signals withinthe constraints of the subaudio band are preferred, because use of thesubaudio band precludes the need for using a dedicated channel fortransmitting the control signals (thereby reducing the number ofavailable channels in the trunked system for voice and datacommunications). A switching protocol is used by the trunked system toautomatically find and engage an open channel when a user initiates atransmission. To maximize the trunking capabilities of such a system,the switching protocol must efficiently allocate channels in the trunkedsystem and avoid channels that are already in use at the time thetransmission is initiated. For further explanation of a conventionaltransmission trunked communication system, reference is made to thedescription of the operation of the ClearChannel LTR® system containedin the manual entitled “E. F. Johnson ClearChannel LTR ApplicationNote”, Part No. 009-0001-020 (Rev. 5, Oct. 1988), available from E. F.Johnson Company, Waseca, Minn., which is fully incorporated by referenceherein. New transmission trunked communications systems have also beenproposed which incorporate advances in network communications. Forexample, the E. F. Johnson MULTINET™ system, part of which is describedin U.S. Pat. No. 5,159,701 to Bames, et al., which is incorporated byreference in its entirety. U.S. Pat. No. 5,159,701 provides for, amongother things, distributively interconnecting a plurality of land mobiletrunked transmission communication systems into a wide area network.

There is a need in the art for a trunked radio communication systemwhich supports large volumes of traffic and which provides efficient andreliable channel allocation.

SUMMARY OF THE INVENTION

A channel assignment system for a trunked radio communication system isprovided to facilitate communications for a plurality of subscribers inthe trunked radio communication system.

Trunked systems require the sharing of a relatively small number ofchannels with respect to the number of subscribers the system maysupport. The large volume of traffic results in collisions betweensubscribers attempting to use the same channels. This is particularlyproblematic where the system employs a “home channel” concept. A homechannel is a system by which subscribers are assigned a particularchannel upon which communications relating to that subscriber areinitially conducted. One problem with the home channel concept is that alarge volume of traffic can result in long delays between a subscriber'srequest for a channel and receipt of a channel to conductcommunications.

Additionally, a large volume of traffic can also result in a splittingof talk groups. A talk group is a collection of subscribers who receivelike instructions for channels to use for reception and transmission inorder to maintain consistency in communications for all subscribers inthe talk group. For example, splitting of a talk group may occur if twoor more subscribers of a same talk group request a channel atapproximately the same time and some of the subscribers from the sametalk group may be directed to conduct communications on differentchannels.

These and other issues are addressed by the various embodiments providedfor by the present system. In one embodiment, the home channels of thepresent system are distributed to avoid excessive use of a singlechannel. In one embodiment, a home channel assignment system is providedto assign home channels to a subscriber in a trunked radio communicationsystem. Home channel assignment is provided for the cases where thesubscriber enters a locality including the preassigned home channel tothe subscriber and where the locality does not include the preassignedhome channel to the subscriber. In one embodiment, the home channel isassigned to the next lower available home channel if the preassignedhome channel is not active in a particular locality. In one embodiment,the home channel is assigned to the next higher available home channelif the preassigned home channel is not active in a particular locality.

In one embodiment, a call grouping system is provided to avoid talkgroup splitting. Upon a channel request by a subscriber having its ownhome channel and talk group, a repeater checks other channels in asystem to ensure that communications for a given home channel and talkgroup are not being conducted on another channel. In one embodiment asingle check is performed for other channels conducting communicationshaving the identical home channel and talk group. In another embodiment,a double check is available for other channels conducting communicationshaving the identical home channel and talk group.

In one embodiment, both home channel aliasing and the call grouping areperformed.

Other embodiments are provided in the detailed description, below, andthe scope of the invention is to be determined by the scope of theappended claims and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a trunked radio communication system,according to one embodiment of the present system.

FIG. 2 is flow diagram for a home channel assignment system according toone embodiment of the present system.

FIG. 3 is a flow diagram for a call grouping system, according to oneembodiment of the present system.

FIG. 4 is a flow diagram for a call grouping system, according to oneembodiment of the present system.

DETAILED DESCRIPTION

In the following detailed description of the preferred embodiment,references are made to the accompanying drawings which form a parthereof, and in which is shown by way of illustration specificembodiments in which the invention may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention, and it is to be understood that otherembodiments may be utilized and that structural changes may be madewithout departing from the spirit and scope of the present invention.The following detailed description is, therefore, not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims and equivalents thereof.

The complete specifications of the following patents and patentapplications are incorporated by reference in their entirety:

U.S. Pat. No. 5,159,701, entitled: METHOD AND APPARATUS FOR ADISTRIBUTIVE WIDE AREA NETWORK FOR A LAND MOBILE TRANSMISSION TRUNKEDCOMMUNICATION SYSTEM, issued Oct. 27, 1992;

U.S. Pat. No. 5,040,237, entitled: RADIO TRUNKING FAULT DETECTIONSYSTEM, issued Feb. 20, 1990;

U.S. patent applications Ser. Nos. 08/400,854, filed Mar. 8, 1995 and08/693,557, filed Aug. 7, 1996, both entitled: PRIORITY SYSTEM FOR AWIDE AREA TRANSMISSION TRUNKED COMMUNICATION SYSTEM;

U.S. Provisional Patent Application Ser. No. 60/047,843, filed May 28,1997, entitled IMPROVED REPEATER COMMUNICATIONS PROTOCOL; and

U.S. patent application Ser. No. 09/058,687, filed Apr. 10, 1998,entitled: TRUNKED RADIO REPEATER COMMUNICATIONS SYSTEM,

A trunked radio system, as defined by the FCC, is a “method of operationin which a number of radio frequency pairs are assigned to radios andbase stations in the system for use as a trunk group”. Trunking is thepooling of radio channels where all users have automatic access to allchannels reducing waiting time and increasing channel capacity for agiven quality of service.

Trunking concepts are based on the theory that individual subscribersuse the system a small percentage of the time and that a large number ofsubscribers will not try to use the system at the exact same time.

In the present system, communications are conducted by subscriberscommunicating with repeaters. For the purposes of this description, asubscriber shall include, but not be limited to, a portable radio, amobile radio, and a handheld radio. Repeaters in the present systemconduct communications which are compatible with an LTR repeater inwhich a logic module performs the call functions and communicates overthe air to the subscriber(s). Each repeater provides a radio frequency(hereinafter “RF”) channel and each repeater contains a logic moduleresponsible for signaling on its own channel. Logic modules then shareinformation with all other repeaters in the system via inter-repeatercommunications. System control is accomplished by the exchange of datamessages between subscriber and repeater. In one embodiment, the systemtrunks up to 20 channels by utilizing continuous subaudible digital dataapplied to the RF carrier simultaneously with voice modulation.Therefore, no dedicated control channel is required and all channels areused for voice communications for system efficiency. Each radio isassigned a home channel which will send system commands to specifiedradios.

The present system may be used in a “locality”. A locality includes aset of repeaters interconnected together to pool the channels in atrunked channel group at a physical site or location. In one embodimentof the present system, each locality has a Status channel. The Statuschannel is used to convey traffic on the system for repeater backuppurposes. The Status channel additionally transmits continuously forsubscriber units that are roaming. The Status channel may also be usedfor voice communications at any time.

Since each repeater is responsible for signaling on its own channel,this approach lends itself well to a distributed processing logiccontrolled approach requiring only a small logic unit within eachrepeater. These processors share information over a communication path.This architecture permits each repeater to be autonomous. A failure inone repeater leaves the remainder of the system intact and running.

In one embodiment, the repeaters are connected to a larger systeminfrastructure. This allows the system to perform some of theaforementioned calls. The system is capable of communicating from oneinfrastructure set to another. In such an embodiment, the systeminfrastructure may be centrally located or distributed at each site or“locality”.

FIG. 1 is a block diagram of a land mobile trunked radio communicationsystem using switches 10 and repeaters 14, according to one embodimentof the present system. The switches 10 utilize a unique signalingprotocol and a switching protocol adapted for communication of controlsignals in the subaudio band. A call router 30 interconnects subsystems,each of which includes, but is not limited to, a switch 10, a pluralityof subscribers 12 for transmitting and receiving transmission trunkedradio communications over one or more channels, and a plurality ofrepeaters 14. In one embodiment, the transmission trunked radiocommunications comprise an information signal and a control signal usingtransmission trunking, with the control signals transmittedsimultaneously in the subaudio range on the same channel over which theinformation signals are transmitted. Switch 10 is used for selectivelyinterconnecting two or more of the repeaters 14 in each trunkedsubsystem, as well as providing the link between other trunked systemsin a wide area network.

In one embodiment, switch 10 is connected to a dispatch console 16 formonitoring the users of subscribers 12 and dispatching calls and othercommunications. Alternatively, a remotely located control station 18 isused to perform the dispatching function on the system. The controlstation 18 may include a selective call console and communications withthe repeater 14 by way of radio communication to the link of the switch10, rather than via a direct or hard-wired connection with the switch10. In addition, switch 10 may be connected with the telephone centraloffice 20 or an external communication network 22 (e.g. a satellitecommunication system or a private PBX system) to allow users on thesystem to make and receive communications or calls outside of thenetwork.

In one embodiment, two or more switches 10 are interconnected by a callrouter 30 that operates as a high speed voice grade communication pathbetween the switches 10. The call router 30 may be any type of matrixswitching equipment or PABX that is capable of handling directed voiceswitching. Switch 10 may also be interconnected to a registrationdatabase 32 for maintaining a database of registration information thatcan be communicated among the switches 10 as a subscriber 12 moves fromcoverage zone to coverage zone. Additionally, one or more of theswitches 10 may be connected to a record monitor 34 for monitoringactivity on the network and performing record keeping, billing and otheraccounting information functions. The activities of the call router 30,the registration database 32 and the record monitor 34 may be containedwithin a single computer linked to each of the switches 10, or may bedistributed among several processors linked to one or more of theswitches 10, depending upon the type of configuration and the functionsthat are required of a particular user's network.

The operation of an independent transmission trunked communicationsystem associated with each switch 10 for one embodiment of the presentsystem will now be described. Control signaling between the repeaters 14associated with a switch 10 and the subscriber 12 is done with subaudiocontrol signals on each channel designated as a “home channel”. Eachsubscriber 12 in the trunked system is assigned to a home channel thatit monitors when the subscriber 12 is not involved in a call. Subscriber12 receives control signal instructions over the home channel to eitherstay on the home channel and open its audio to receive a call, or tochange to a different channel and open its audio to receive a call. Ifthe subscriber 12 is sent to another channel to receive a call, it willreturn to its home channel as soon as the call is completed.

When a subscriber 12 wants to initiate a call, all the operator has todo is depress the push-to-talk (PTT) button and hold it. If the homechannel assigned to subscriber 12 is available, the transmitter forsubscriber 12 will transmit a control signal on the home channelfrequency telling the repeater 14 that a call is being setup on thatchannel. At that point, the subscriber 12 turns its transmitter off andwaits for a return message from the repeater 14. If the repeater 14 isnot busy, the repeater 14 will broadcast a handshake message that willbe received by all subscribers 12 assigned to the same home channel. Theoperator of the initiating subscriber 12 will hear an audible proceedtone and its transmitter will be enabled to proceed with the call. Forthis type of group calling, all other subscribers 12 with the correctgroup identification will remain on the channel and open their squelchto receive the call. All subscribers 12 that did not have the propergroup identification would remain muted, but the logic unit of thesesubscribers 12 would receive and store the control signal indicatingthat their home channel was now busy and that they would get a freechannel assignment. As a result, if a subscriber 12 not involved in thecall described above now wanted to initiate a call, it would know wherea free channel was so that it would not have to look for a free channelin the trunked system.

If the home channel for a subscriber 12 was busy when a call wasinitiated, the initial data transmission would be made on the freechannel that it had stored in memory. The repeater 14 receiving the callwould notify the repeater 14 for the home channel assigned to thesubscriber 12 initiating the call that a call was being setup on thefree channel for a group assigned to the home channel repeater 14. Thehome channel repeater 14 would then add this information to the controlsignal being sent out over the home channel, and would also change thefree channel assignment to another free channel. The subscriber 12 thathad a proper group assignment would receive the control signal sent outover the home channel that a call was being setup for their group on thedirected channel and would switch to that channel and open their squelchto receive the call. All other groups 12 that did not have the propergroup assignment would store the free channel information and wouldcontinue to monitor the home channel.

Channel Distribution of Subscriber Units

In one embodiment of the present system, home channel assignments aredistributed over all home channels or at least a majority of them at alocality. The repeaters in the system transmit a code which identifiesfree channels, which are channels available for communications. Thechannel where subscriber units reside, the number of channels that thetotal subscriber population is distributed over, and the backup channelcapabilities are addressed differently. These issues impact access time,call handling, and collision probability. FIG. 2 shows a flow diagram ofone embodiment of the channel distribution system.

Subscriber Unit Distribution

The total subscriber population is distributed over several ‘home’channels. If the units are spread over multiple ‘home’ channels then thecollision probability is reduced. This is due to the increasedprobability of different channels outputting different ‘free’ channels.This requires that the subscribers strive to monitor or reside on theirgiven ‘home’ channel.

The subscriber unit and system have the ability to use an alias homechannel when the specific channel is not defined and used at a givenlocality. This provides uniform home and talk group assignment over atotal system with multiple locality coverage, and eases the burden ofhome and talk group usage for a system administrator.

Alias Home Channel

The alias home channel function allows subscriber units that areprogrammed for a given home channel a method to select another homechannel or alias home channel for sites where the programmed homechannel is not available. In one embodiment, the next lowest definedchannel on a locality (set of repeaters) becomes the alias home channeland is monitored for its home channel traffic. This allows spreading ofthe subscriber units across the multiple channels on a locality and notplacing all the non-defined home subscriber units on a single channel,such as a status channel. This reduces collision probability on thesystem. In one embodiment, this function is accomplished by distributedhome channel numbering and by the subscriber units going to the nextlowest defined channel to monitor. Distributed channel numbering is thedistributed assignment of home repeater numbers so that subscribersusing intervening channels are distributed among the home channelassignments. For systems where each repeater supports a single channelthe distribution of channels amounts to a distribution across actualrepeaters.

For example:

5 channel system: 1 5 9 13 17 10 channel system: 1 3 5 7 9 11 13 15 1719 15 channel system: 1 2 3 5 6 7 9 10 11 13 14 15 17 18 19 20 channelsystem: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

The numbering of home repeaters allows a repeater that is acting as analias to carry an equal load of the aliased channels. In the 5 channelsystem repeater 1 will act as the home for 2, 3, and 4; repeater 5 willact as the home for 6, 7, and 8, and so on.

For example, a subscriber unit programmed for home 12 on a 5 channellocality (numbered per the above chart) knows there is no channel 12defined for the locality and will look for next lowest defined channel,number 9. When the subscriber unit roams into the 5 channel locality theunit will move to channel 9 to monitor for activity. In this example,repeater 9 is programmed such that if repeater 10, 11, and 12 are notactive for the locality, then repeater 9 is the “alias” for repeaters10, 11, and 12. When repeater 9 sees activity on the inter-repeatercommunications that another repeater is active with units from homes 10,11, and/or 12, repeater 9 will act like the home for those repeaters andoutput the trunked traffic accordingly. Repeater 9 is reprogrammed forthe proper aliasing if repeater numbering is changed.

Other aliasing techniques may be employed without departing from thescope and spirit of the invention. For example, instead of going to thenext lowest available channel, the aliased home channel could be thenext highest available channel.

Call Grouping

In one embodiment of the present system, the repeaters are programmed toconduct communications on a single channel for a single talk group toavoid talk group splitting. Talk group splitting occurs when two or moresubscriber units of the same talk group attempt to access the system atapproximately the same time on different channels. Both units maysuccessfully handshake and, unless the repeater system assists,alternating collections will be made causing some units to go to onechannel and other units to go to the other channel or, units may switchbetween the two channels.

A subscriber unit that is attempting to access a channel and receives arepeater response with the same home and talk group code but the channelin use is a different channel (or different repeater in cases where eachrepeater supports a single channel) should stop the channel acquisitionand go to the channel (or repeater) in use and begin the receiveprocess.

Since the subscriber unit operates in the manner stated in the aboveparagraph the repeater must operate to accommodate the above action.Again, in the case where each repeater supports a single channel, achange in the channel is related to a change in the actual repeater usedto conduct communications. This operation is shown in FIG. 3 for oneembodiment of the present system.

As shown in FIG. 3, when a repeater receives an initial group calltransmission from a subscriber unit, the repeater shall look to see ifany other channel is busy with that specific home and talk group. Ifthere are none then the present repeater shall grant access by returningthe same home and talk group codes with the channel in use being that ofthe present repeater. If another channel is busy with that specific homeand talk group, then the subscriber is directed to that channel toconduct communications.

FIG. 4 shows one embodiment in which a dual testing format is performedto collect subscribers to a single channel. In this embodiment, a firstcheck of available channels is performed after the subscriber requests achannel. If a second channel is found which uses the same home and talkgroup, then the subscriber is directed to the second channel forcommunications. However, if no other channels are found to becommunicating using the same home and talk group, then the presentchannel is granted temporarily for use. A second test is performed afterthe temporary grant of the present channel to determine if anotherchannel is conducting communications using the same home and talk groupinformation. Once the repeater temporarily grants the subscriber thechannel the repeater communicates with the other repeaters. When therepeater attempts the initial inter-repeater communication, transitionsfrom idle to busy with its local traffic at its transmission period, therepeater looks to see if the specific home and talk group is active onanother channel. If no other channel using the same home and talk groupinformation is found, then the present channel is fully granted for theduration of the call. Otherwise, if there was another channel activewith the specific home and talk group at the initial inter-repeatercommunication then the present repeater shall change the channel in usethat is being transmitted to the other active channel/repeater. Thepresent repeater will operate as if the specific home and talk group istrunked traffic for the duration of the transmission from the subscriberunit. The second test accounts for the asynchronous nature of channelrequests in a trunked radio system.

System Operation

Home channel distribution and aliasing and call grouping may beperformed by any protocol which communicates home channel, talk group,channel in use and free channel information. For example, in LTRsystems, which are explained in U.S. Pat. No. 5,159,701, and the otherdocuments incorporated by reference above, home channel information isprovided by the LTR HOME code; channel in use information is provided bythe LTR GO TO code; free channel information is provided using the LTRFREE code; and talk group information is provided using the LTR ID code.

In LTRNET™ systems, which relate to the NP system discussed in U.S.Provisional Patent Application Ser. No. 60/047,843, entitled IMPROVEDREPEATER COMMUNICATIONS PROTOCOL, and U.S. patent application Ser. No.09/058,687, filed Apr. 10, 1998, entitled TRUNKED RADIO REPEATERCOMMUNICATION SYSTEM, which were incorporated by reference in theirentirety, above, home channel information is provided by the NP HOMEcode; channel in use information is provided by the NP ChiU code; freechannel information is provided using the NP FREE code; and talk groupinformation is provided using the NP GROUP code.

In MULTINET™ systems, which are also discussed in the incorporateddocuments, including U.S. Pat. No. 5,159,701, home channel informationis provided by the MULTINET™ HOME code; channel in use information isprovided by the MULTINET™ GO TO code; free channel information isprovided using the MULTINET™ FREE code; and talk group information isprovided using the MULTINET™ GROUP code.

Those skilled in the art will readily recognize that other protocols maybe used without departing from the scope of the present invention.

Home channel distribution and aliasing and call grouping may be usedseparately or in combination by a trunked repeater system. In a systemwhich uses home channel distribution and aliasing and call grouping incombination, the repeaters are programmed to track and monitor thealiased home channels to perform call grouping. Further information maybe found in U.S. patent application Ser. No 09/056,687, filed Apr. 10,1998, entitled TRUNKED RADIO REPEATER COMMUNICATION SYSTEM, which wasincorporated by reference in its entirety, above.

The foregoing description is intended to demonstrate embodiments of thepresent invention. One skilled in the art will readily recognize thatsystems having different names, codes and procedures are taught by thepresent teachings and do not depart from the scope of the presentinvention. The teachings herein are not to be taken in an exclusive,exhaustive, or limiting sense, but are provided to describe differentmodes of the present invention, and the scope of the present inventionis given by the attached claims and their equivalents.

What is claimed is:
 1. A method comprising: selecting a first subset ofprimary home channels from a plurality of candidate channels;configuring each of a plurality of repeaters within a locality tomonitor a primary home channel, wherein each primary home channel ismonitored by a particular repeater of the plurality of repeaters;receiving a subaudio message on a particular alias home channel selectedfrom a second subset of alias home channels selected from the pluralityof candidate channels, wherein each alias home channel is associatedwith a primary home channel; and if the primary home channel associatedwith the particular alias home channel is available for communications,conducting communications on the primary home channel; and otherwise,seeking a next available channel.
 2. The method of claim 1 whereinreceiving a subaudio message includes receiving subaudible digital data.3. The method of claim 1 wherein receiving a subaudio message includesreceiving subaudible digital data simultaneous with voice modulation. 4.The method of claim 1 wherein receiving a subaudio message includesreceiving a control signal.
 5. The method of claim 1 further comprisingtransmitting to a roaming subscriber within the locality.
 6. The methodof claim 1 further comprising transmitting a subaudio signal to aroaming subscriber within the locality.
 7. The method of claim 1 furthercomprising transmitting a control signal to a particular subscriber. 8.The method of claim 7 wherein transmitting a control signal to aparticular subscriber includes transmitting an instruction to remain ona particular channel.
 9. The method of claim 7 wherein transmitting acontrol signal to a particular subscriber includes transmitting aninstruction to change to a particular channel.
 10. A method comprising:receiving a first wireless subaudio control signal from a firstsubscriber having a first group identification code, the first controlsignal including a request to communicate; and transmitting a handshakesignal to the first subscriber and a second subscriber having theparticular home channel assignment, a squelch, and a second groupidentification code, wherein if the second group identification codematches the first group identification code then the handshake signalinstructs the second subscriber to open the squelch and wherein if thesecond group identification code is different than the first groupidentification code, then the handshake signal instructs the secondsubscriber to close the squelch and await a second subaudio controlsignal instruction indicating that the particular home channel is busyand a free channel assignment.
 11. The method of claim 10 furthercomprising transmitting the second subaudio control signal instructionindicating that the particular home channel is busy.
 12. The method ofclaim 10 further comprising transmitting the second subaudio controlsignal instruction including a free channel assignment.
 13. The methodof claim 10 wherein receiving a first wireless subaudio control signalfrom a first subscriber includes receiving a first wireless subaudiocontrol signal on a particular home channel assigned to the firstsubscriber.
 14. The method of claim 10 wherein receiving a firstwireless subaudio control signal from a first subscriber includesreceiving a first wireless subaudio control signal on a free channelassigned to the first subscriber.
 15. A method comprising: uniformlydistributing candidate home channel numbers across a range of availablechannel numbers; assigning a home channel to each subscriber; receivinga subaudio message on a particular candidate home channel numbercorresponding to a particular home channel assigned to a particularsubscriber; if the particular home channel is a candidate home channelnumber, conducting communications on the particular home channel; andotherwise, seeking a next available candidate home channel number. 16.The method of claim 15 wherein seeking a next available candidate homechannel number comprises scanning the candidate home channel numbersbelow the assigned home channel.
 17. The method of claim 15 whereinseeking a next available candidate home channel number comprisesscanning the candidate home channel numbers above the assigned homechannel.
 18. The method of claim 15 wherein conducting communicationsincludes communicating home channel information using a home code, openchannel information using a free channel code, and channel in useinformation.
 19. The method of claim 15 wherein conductingcommunications includes conducting voice communications.
 20. The methodof claim 15 further comprising: upon receipt of a group calltransmission from the particular subscriber on a first channel, checkingfor a second channel conducting communications having an identical homechannel and an identical talk group; and if a second channel exists,instructing the particular subscriber to use the second channel forcommunications.
 21. The method of claim 20 further comprising if thesecond channel is conducting communications using a home channel aliasassociated with the identical home channel and the identical talk group,instructing the particular subscriber to use the second channel forcommunications.
 22. The method of claim 20 further comprising if thesecond channel does not exist, allowing the particular subscriber toconduct communications on the first channel.
 23. The method of claim 20further comprising if a second channel is not found, temporarilygranting the first channel for use by the particular subscriber andperforming a second test to determine if the first channel is fullygranted.